Removal of fine dust from bauxite



UNITED STATES OFFICE REMOVAL OF FINE DUST FROM BAUXITE Ferdinand W. Broth and Anthony Kinsel, Petrolia, Pa., assignors to L. Sonneborn Sons, Inc., New York, N. Y., a corporation of Delaware No Drawing. Original application March 14,

1939, Serial No. 261,790. Divided and this application November 9, 1943, Serial No. 509,630

4 Claims. (01. 23-142) 1 2 This invention relates to adsorbent bauxite adsorbent properties, and acquires enhanced adand to a method for preparing adsorbent bauxite sorbent properties only after heat treatment of improved characteristics. which is generally referred to in the industry as The present application is a division of our the activation of the bauxite. Before being subapplication Serial No. 261,790, filed March 14, 5 jected to heat treatment, the raw bauxite is 1939, entitled Bauxite adsorbents and processes usually ground and screened to produce material of making d using same. having a particle size predominantly between 20 The conventional liquid phase refining treatand 80 mesh, bauxite within this range of parment of petroleum hydrocarbons including resiticle size having been found particularly adapted due and distillates, such as kerosene, gasoline, to the treatment of oil by the percolation techlubricating oils, transformer oils, medicinal oils, nique. Particles coarser than 20 mesh, as a generpetrolatum, parafiin, etc., generally involves the al rule, (10 not exhibit the high adsorptlve use of solid adsorbent materials to improve the ciency necessary for successful percolation, while color of such products or to eifect a partial p i l s sm ll r t an 80 m h, o h possessing desulphurization of the same. For this pur ose adsorptive characteristics to a high degree, W111 the hydrocarbons are brought into contact with give unsatisfactory yields as a result of lncreased the adsorbent material. This may be accomsoakage, and furthermore will result in the forplished in various ways, such as by admixing the mation of filter beds so dense that the filtration adsorbent material in a finely divided form with rate is materially impairedthe hydrocarbon to be refined and thereafter se The activation of the bauxite is usually cararating the mixture by means of a filter press ried out by heating the same to temperatures of which retains the adsorbent material, which the order of from 600 to 1600 F. Such treatprocess is commonly referred to as contacting, ment p s 0 the b t ce ds por, alternatively, by passing the hydrocarbon mative pr p which y be regenerated after terial through abed of the adsorbent from which he baux te becomes exhausted during use, by it issues in a decolorized condition. The latter again roasting Same at temperatures of the Order procedure is commonly referred to as "percola- 0f the magnitude aforesaidtion. If the hydrocarbon to be refined is solid During the act t of bauxite by heat treator semi-solid at ordinary temperatures, such as ment at temperatures t n 600 and 0 parafiin, petrolatum, and like substances, it is a general diminution in size of the particles subcontacted with the adsorbent material, preferjected to the treatment occurs and an appreciable ably in molten condition or dissolved in a suitamount of particles finer than 80 mesh is proable solvent. The term decolorized or such simduced. We have found that, although most of ilar expression as used in the industry and in this these particles below 30 mesh, which particles for application does not necessarily connote the re- P p s Of Convenience may be termed t moval of visible coloring matter only. It also dust, a e removable y mechanical s, v

connotes improvement of the original color by vir screen sifting and the like, comparatively large tue of removal of colorless. compounds which amounts are retained by the coarser bauxite parare converted to visible coloring matter by the ticles and cannot be removed by such means. We polymerizing action of the adsorbent material. have discovered that this phenomenon is due The adsorbent material principally used in the to the fact that an activated bauxite possesses industry in the percolation method is generally a pronounced power of attraction for its own a clay of the fullers earth type which has been dust, and will usually exercise this power of specially processed to develop its adsorbent charattraction to the extent of causing retention of acteristics; for example, it may be subjected to up to 10 per cent of bauxite dust (calculated on heat or acid treatment or both. the total amount of bauxite present after separa- Percolation through bauxite has been used to tion of the conventionally removable dust). We some extent for the refining of some petroleum have found that the adsorptive eificiency of achydrocarbons. Bauxite, however, as it is obtivated bauxite of a particle size between 20 and tained from the mine, possesses only very weak 5( mesh for the refining of hydrocarbon prod-.

note is greatly impaired and materially reduced by reason of these dust particles which tenaciously adhere to the particles of larger size despite the fact that the dust particles, as such, inherently possess an adsorptive efiiciency which is superior to that of bauxite particles of coarser mesh size. The adsorptive efficiency of bauxite particles of a size between 20 and 80 mesh progressively decreases with the presence of increasing amounts of particles smaller than 80 mesh until a minimum is reached at a point where the dust content of the bauxite reaches approxi mately per cent. With higher dust contents the adsorptive efficiency again commences to increase as the amountflof dust present in excess of approximately 10 per cent commehcs to add its inherent adsorptive efficiency to that ofthe coarser bauxite particles, the efficiency of which is impaired by reason of the first 10 per cent dust found to be tenaciously adhering to the coarser particles. With a dust content of approximately 25 per cent, the adsorptive efficiency of the dust containing bauxite will have again reached the adsorptive efficiency of substantially completely dedusted bauxite, and will further increase with increasing dust content. Though from the standpoint of adsorptive eiiicieriy the presence of large amounts of dust may be desirable,- we have found that dust will interfere with the successful per colation treatment to such-an extent that the removal of the dust present in excess of and preferably in excess of1;0 per cent is a prerequisite to succe'ssful bauxite filtration with regard to fil-' tration yield and rate of how of the hydrocarbon material through the filter bed. 4

In the following table, the a'dsorptive efficiency of a bauxite of a particle size between and 80 mesh and containing varying amounts of dust, is shown:

TABLE! Adsorptioe emcien of bdufr'iie' commandant/mo amounts" of dust Per Cent Dust H OCAIMMHH OOUIOCHOUIO As shown in the table, the adsorptive tendency of the bauxite or the dust (last horizontal column), respectively, is'expressed in terms (if grav ity test; The term gravity test of a partieuiar' adsorbent material, as developed by one of us to express adsorptive efficiency of such material, connotes, with the omission of decimals, the diffei'ence between the respective specific g'ravities of the hydrocarberi-materialto here-fined before and after its filtration through the adsorbent. Sincefor a successful percolation treatment a dust content in excess 'of 15 per cent and prefer ably in excess of 10 per 'cent is undesirable, and since up to 10 per cent of dust content consti-- tutes an impairment of the adsorptiv'eeificiency of the filter material, itisrequi'site for efficient per: colation operations tofemove substantially all of th'e'dust including the-portion adhering to the coarser particles.

We have discovered that the-attractive power of the bauxitefo'r its own dust varies with certain temperatures arid that a temperature range of minimum attraction exists within which the attractively adhering bauxite dust may be removed from the bauxite by suitable means, such as a blast or current of air or other suitable gas. This temperature range of minimum attraction of bauxite for bauxite dust lies between 500 and 1600 F., and preferably between 600 and 1200 F. When blowing air over or through the bauxite within this temperature range and preferably in counter-current fashion, the attractively adhering bauxite dust is substantially completely removed, and we have termed and will hereafter refer to such temperature ranges as the effective dedusting temperature range of the bauxite. For the purpose of preventing the cooling of the bauxite to below the effective dedusting temperature range prior to the substantially complete removal of attracted dust, we prefer to preheat the air before blowing the same over or through th bauxite, and have found that best results and a substantially dust-free bauxite are obtained by not only maintaining the bauxite within the effective dedu'sting temperature range but also passing the air over or through the bauxite after the air has been heated to a temperature of at least 120 F.,- and preferably of at least 220 F. The current or blast of air or other suitable gas passing over or through the bauxite should have a velocity sufficient to remove the dust particles from the bauxite while the same is within the effective dcdusting temperature range. With air velocities of from 4 to 6 feet per second, and a preferred velocity of 5 feet per second, satisfactory results are obtained.

The conditioning of bauxite in accordance with our invention is preferably carried out in the following manner: The bauxite ore is first roasted in accordance with-conventional practice by heating the same in a suitable furnace or kiln, such as a Herreshoff type furnace, a rotary kiln, a vertical stationary furnace, or the like, to a temperature of from 600 to 1600 F., and preferably to a temperature of from 1000 to 1200 F. Assuming that a multi-hearth Herreshoff furnace is being used, heat is applied to the various hearths preferably in such manner that the temperature of the ore on each hearth is raised by suitable increments F. to F.- in the case of a 12-hearth furnace) until the desired-temperature is reached on the last hearth. During the roasting operation sufiicient air is admitted to maintain good oxidizing conditions in all parts of the furnace at all times, the throughput being preferably regulated in such manner that not more than approximately a 24mph layer of the ore is carried by the hearth arms, which may be rotated, for example, at a speed of approximately 6 revolutions per minute.

Following the roasting operation the calcined bauxite is next subjected to the dedusting treatme'nt which is preferably carried out in a closed receptacle through which a'stream of hot baux-' ite is passed either in a vertical column by means of gravity, as for instance in cascade fashion or, horizontally by means of conveyors, being met in its travel and whileits temperature is within the effective dedusting temperature range of from 500 to 1600 F., by an air current (preferably pre heated) of a velocity of from 4 to 6 feet per second,-and preferably of 5 feetper second. The effective dedusting temperature range is best maintained by passing the bauxite into the receptacle which may be, for example, a cascade tower of about 30 feet in height, at a temperature as 169.! as possib1e to the preferred upperlimit of the effective dedusting temperature, 1. e., 1200 F., or at a slightly higher temperature. The air or other suitable gas is passed countercurrently over or through the bauxite in such manner that, at the point of first contact of the stream of air with the bauxite, and while the bauxite is still within the effective dedusting temperature range, the air is at a temperature preferably of from 120 to 220 F., and at the point of last contact with the bauxite, i. e., at the bauxite feed end of the receptacle, the air is at a temperature of at least 200 F., and preferably of at least 250 F. The dust carried away by the countercurrent stream or blast of air or other suitable gas is precipitated and discharged into a storage bin or tank or, if desired, directly into one or more filter towers.

The changes effected in a bauxite subjected to treatment in the afore-described manner are illustrated by the following Tables II and III. Table II shows the average mesh content of an original ore and that of the activated material, while Table III illustrates the change in composition resulting from the treatment.

TABLE II Bauxite Activated Mesh Ore, Bauxite,

Per Cent Per Cent On 80 i. 3 3 Through S traces TABLE III Bauxite Activated Ore, Bauxite, Per Cent Per Cent Moisture Loss (5) 110 C 1.0 Combined Water 29.0 1.5 Soluble Alumina as A1203. 56. 0 80. 0 Soluble Iron as FezOa... 5.0 o. 0 Soluble Titanium as TiO 1.0 1.0 Insoluble Residue 8. 0 1 1.5

From Table II it will be noted that while the treatment results in a general diminution 0f particle size the percentage of particles finer than 80 mesh is reduced to mere traces.

The superiority in oil treatment operations of bauxite which has been treated according to the invention is illustrated by the following examples:

EXAMPLE I A Pennsylvania neutral oil having a specific gravity of .8620 was percolated through bauxite activated in accordance with prior practice and containing 11-10 per cent of dust attractively adhering thereto, and through a substantially dust-free bauxite prepared in the afore-indicated manner. The loss in specific gravity which as indicated hereinbefore is a measure of the adsorptive efiiciency of an adsorbent was greatest inthe case of a. dust-free material. The results of the tests are summarized in the table below:

TABLE IV Per Cent Dust Gravity The second column of the table shows the respective gravities of the stock after filtration through bauxite containing dust in the amounts indicated in the first column, while the third column shows the respective gravity test numbers.

EXAMPLE ]I A Midcontinent Bright Stock was respectively percolated through a bauxite activated and dedusted in accordance with our invention and through a bauxite activated without removal of adhering dust particles, at a temperature of 250 F., and under atmospheric pressure. The respective bauxites possessed the following character- A comparative analysis of the qualities of the aforementioned stock before and after filtration through the respective bauxites is given in the following table:

TABLE V Filtered Filtered through through Original Activated Activated 60 Dedusted Undedusted Bawnte Bauxite EXAMPLE III teristics:

Screen Analysis Gravity Dust FezO; Test Per Gen! Per Cent Stabilized Bauxiten 1 29 40 28 3 Activated Unstabihzed Bauxite" 2 6.0 98 30 40 27 3 The roiiowmgtabie-snowsa c'bmp'arative anais'e sis ofthe properties ofthe stock'before and after filtration through therespective bauxites:

When the adsorptive efficiency of bauxite has been exhausted through continued use in the treatment of oil, the same need not' be discarded but may Ice-reactivated. The reactivation may be conducted with or without the prior removal of' retained hydrocarbons by means of suitable solvents such as naphtha; by roasting the bauxite at an elevated temperature, andpreferably between 600 nd. 1600 F, whereby the adsorbed organic matter is carbonized and substantially completely removed by maintaining an oxidizing atmosphere in the furnace or kiln during the roasting operation. This reactivation or regeneration of the bauxite and its subsequent re-use as an adsorbent refining material may b carried out repetitiously.

Just as in the initial activation of raw bauxite, the reactivation of partially or completely spent bauxite is accompanied by the formation of considerable quantities of dust, a part of which may be of adherent character. The amount of dust formed will be less if. the reactivation treatment has been preceded by the removal of retained hydrocarbons, the presence of which. appears to contribute to the friability of the bauxite under the conditions of. the reactivation treatment. In any event it is highly desirable that the adherent dust as well as the non.- adherent dust be removed from the reactivated material for the reasons previously given. This may be readily accomplished by the method described herein.

The term activated bauxite as used in the appended claims encompasses reactivated or regenerated bauxite as well as bauxite which has been subjected to only a single activation treat ment.

We claim:

1. A process which comprises contacting activated bauxite predominating in particles of a particle size withinthe range of 20 to 80 mesh at a temperature of from 1000'F. to 1200 F. with a current of preheated air having a velocity of from. 4 to 6 feet per second to substantially free said particles of adherent relatively finer particles inseparable therefrom. by screening, said 8; 'air being at a temperature of' fi'onr 120F1 to-220 F. at the point offirst contact with said bauxite and at a temperature of from 200 F. to 250 F. at the point of'l'ast contact with said bauxite.

2. A process which comprises contacting activated bauxite predominating in particles of a particle size within the range of 20 to mesh at a temperature of'from 1000 F. to 1200 F. with a current of preheated air having a velocity of from 4.- to 6'feet per second tosubstantially free said particles of adherent relatively finer particles inseparable therefrom by screening.

3; A process which comprises contacting activated bauxite predominating in particles of a particle size within the range of 20 to 80 mesh at a temperature of from 1000 F. to 1200 F. with a current of preheated air having a, velocity of from 4 to 6 feet per second to substantially free said particles of adherent relatively finer particles inseparable therefrom by screening, said 'air being preheated to a temperature between F. and 220 F. prior to contacting with the bauxite.

4. A process which comprises contacting activated bauxite predominating in particles of a particle siz within the range of 20 to 80 mesh at atemperature of from 500 F. to 1600 F. with a current of preheated air having a velocity of from 4 to 6 feet per second to substantially free said particles of adherent relatively finer particles inseparabl therefrom by screening, said air being preheated to a temperature between 120 F. and 220 F. prior to contacting with the bauxite.

FERDINAND W. BRETH. ANTHONY KINSEL.

REFERENCES CITED The following. references are of record in the file of this patent: 1

UNITED STATES PATENTS Number Name Date 2,006,693 Hechenbleikner July 2, 1935 2,107,215 Rembert Feb. 1, 1938 2;016,271 Buellet al. Oct. 8, 1935 2,160,874 Kinsel June 6, 1939 FOREIGN PATENTS- Number Country Date 236,263 Great Britain June 29, 1925 416,711 Great Britai Sept. 13, 1934 OTHER REFERENCES Shaw, Air Separation Methods used in Fine Grinding of Rock Products, pp. 25-26. Reprint from Rock Products for Oct. 15, 1927. I

Berri'sford et al., Pneumatic De-dusting of coal, Transactions of the Institution of Mining Engineers, London, vol; 89; p. 328, Sept, 1935. 

